Pigment paper coating composition



United States Patent 25,884 PIGMENT PAPER COATING COMPOSITION Thomas L.Reiling, Dedham, Mass., assignor to Blandin Paper Company, Grand Rapids,Minn., a corporation of Minnesota No Drawing. Original No. 3,002,844,dated Oct. 3, 1961, Ser. No. 856,383, Dec. 1, 1959. Application forreissue Oct. 1, 1963, Ser. No. 327,858

12 Claims. (Cl. 106-128) Matter enclosed in heavy brackets appears inthe original patent but forms no part of this reissue specification;matter printed in italics indicates the additions made by reissue.

The present invention relates to [the manufacture of coatings for paper]paper coating, and more particularly, to [a] paper coating compositions,and [having many of the desired properties and advantages of a so-calledcast coating] to papers coated therewith.

Cast coatings, which are obtained by casting the coating material on apolished drum and releasing the coating material from the drum to thepaper, are used in most instances where smooth, bright, glossy,ink-receptive papers are required. Many thousands of tons of paperhaving these properties, which are hereinafter referred to aseye-appeal, are required each year for labels, magazine covers, stockfor printing advertising matter, and stock for other similar purposes.Such stock is expensive, because its production is slow and the capitaloutlay required for the machinery necessary for cast coatings is verygreat. Consequently, the art has long sought suitable substitutes forcast coated paper stock, but to the best of my knowledge, heretofore nosuch substitute has been available.

It is, therefore, the object of this invention to produce a coatingcomposition which may be applied to paper stock by conventional coatingequipment and which provide a sheet of paper stock having the propertiesof a cast coated sheet.

A further object of this invention is to provide a coating compositionfor paper stock, which may be applied at greater speed than cast coatedcompositions, and which will provide a sheet having eye-appeal, ashereinabove defined.

A further object of this invention is to provide a coating for standardfine printing papers which does not re quire calendering.

A further object of this invention is to provide compositions which canbe applied to paper using conventional paper coating equipment in a verythin or lightweight layer to achieve great gains in opacity or lightrefraction, and which can be supercalendered to produce superiorlightweight printing papers.

A further object of this invention is to provide methods for introducingpigment into a liquid hydrocarbon-inwater emulsion containing dissolvedprotein.

A further object of this invention is to provide new types of coatedpapers and the like produced using the coating compositions of thisinvention and conventional paper coating techniques.

Still further objects and advantages of the invention will appear fromthe following description and appended claims.

The invention is based on the surprising discovery that a composition ofmatter prepared by intermixing two [components,] separately preparedformulations, the first formulation containing [consisting of an] alkalisoluble, water insoluble protein, [oil] liquid hydrocarbon and water inthe form of an emulsion, and the second [consisting of a] formulationcontaining water soluble gum, [such as glue, a] paper pigment [materialsuch as clay or other filler] and water [results in the formation of aRe. 25,884 Reissued Oct. 19, 1965 ice suspension of a protein coatedpigment composition having] in the form of a suspension, hasexceptionally good paper coating characteristics. My composition has adesirably high solids content and may be applied to paper stock byconventional paper coating machinery and thereafter dried to a generallyhard, bright, glossy, smooth surface which has improved ink receptivityand varnish holdout, yielding, for example, an excellent high glossprint. Because my novel coating composition may be applied to paper websby conventional paper coating machinery, paper coated in accordance withmy process may be coated at much greater speeds than paper coated withthe so-called casting process.

The advantages of using an emulsion of water and [oil] liquidhydrocarbon in combination with an alkali soluble, water insolubleprotein to provide a coating having improved opacity and brightness,were first taught by Kress et al., US. Patent #2,339,707. However, theKress invention is subject to several serious limitations, in that theoil-water-protein ratios must be such that the solids content of thecoating is insufiicient to enable the coating to be used economically inmodern coating machinery. [The] Furthermore, the direct addition offinely divided, water insoluble, and liquid hydrocarbon insoluble solidsto the protein, petroleum, water emulsion recommended by Kress resultsin an appreciable loss of brightness, opacity, and gloss when as littleas 3% of pigment or filler is incorporated in the mixture. However, Ihave found that the addition of a suspension of a paper pigment inaqueous solution of a water soluble gum such as animal glue, vegetableglue, or other water soluble gum, and a pigment, when first mixedtogether and thereafter added] to a protein, oil, water emulsionpreserves the desired paper coating properties of opacity, brightness,printability, and gloss obtained by using an alkali soluble protein, oiland water emulsion, and at the same time, enhances the scuff-resistantproperties and provides a relatively high solids content for thecomposition, so that it may be used in conventional coating machinery.

In this specification I use the words, paper pigment [and paper fillerinterchangeably. By these words I mean] to include the finely subdividedsolid, substantially insoluble, materials which are commonly used forsurface treating of paper sheeting, including but by no means limited tochalk, talc, calcium carbonate, clay, walnut flour, titanium [,1dioxide, satin White, and the like, and any mixtures of these. [These]As those skilled in the art will appreciate, paper pigments aresometimes distinguishable from the so-called coloring pigments both inpurpose and in utility,] Since the coloring pigments such as iron oxide,umber, carbon black, copper oxide and the like [would] frequently socolor the emulsion as to make it of little value in paper coating. Also,these coloring pigments would provide little if any filler action on thesurface of the raw paper sheet material and therefore are [inoperable]commonly unsuitable for the purpose of this invention.

1 use the term alkali soluble, water insoluble protein in the same senseas it is used in the above referred to Kress et al. patent to refer to aconventional proteinaceous material which dissolves in aqueous solutionhaving a pH above 7. Examples include isolated soya proteins in eitherunmodified or modified forms, casein, and any mixtures or equivalentsthereof. The preferred alkali is ammonium hydroxide, but this canoptionally be replaced in whole or in part by any other alkalis normallyemployed for dissolving water insoluble proteins.

By the word "gurn I have reference to the conventional meaning of thisterm in the paper industry whereby reference is had to a generally highmolecular weight,

organic material of natural or synthetic origin which is water solubleand adapted for use as an adhesive. Thus, the term includes animalglues, vegetable glues (starches such as potato dextrin) polyvinylalcohol, methyl cellulose, and any mixtures and equivalents of thesesubstances.

The term "liquid hydrocarbon I use herein in its conventional sense torefer to an inert, oily, water insoluble, volatile liquid chemicallyconsisting substantially of carbon and hydrogen.

Going into more detail, I have found that by [forming] mixing anemulsion of a hydrocarbon [J in water and a] containing a dissolvedalkali soluble, Water in soluble protein [and thereafter adding] with asuspension of water, a paper pigment [of the type heretofore defined,water] and a dissolved gum, [such as animal glue,] I provide a surfacecoating for papers which is smooth, highly ink-receptive, has gloss andbrightness characteristics which are comparable to the most expensivecast coatings, and is more scuff resistant (i.e. resistant to marring orsurface deformation, when brought in contact with or abraded by foreignmaterials), than are the most cxpensive heavily pigmented papercoatings. [I have found] While I do not wish to be bound, I believe frommy UhSttl'tltlOltS that when one of my emulsion-suspensions is broken,as by evaporation of the volatile components, an alkali soluble, waterinsoluble protein will precipitate as fine [d] particles and adhere tothe surface of the pigment particles and change the character of thepigment surface from a dull, semi-translucent and extremelyink-receptive surface to a surface having high gloss, excellent opacityand controlled ink receptivity. The protein particles which adhere tothe pig ment particles and co-precipitate onto the surface of the paperwhen the emulsion is broken, provide a paper coating having the desiredcharacteristics. Furthermore, unlike the usual pigmented coatings, thecoating compositions of my invention are more resistant to the deeppenetration of oil or varnish present in ink, and thereby reduce theamount of ink required for surface coverage and reduce the drying timeof the ink required for surface coverage of the sheet. Paper coated withthe compositions of my invention resists the tendency of ink to showthrough the paper, because of higher opacity of the surface and becauseless ink is required to accomplish the same result, and this latterproperty, the ability to retard ink absorption, I refer to as improvedvarnish hold out.

[My composition comprises] As indicated, my compositions are produced bymixing an emulsion with a suspension. The emulsion contains betweenabout 5 and [2O] parts of [an] dissolved alkali soluble-water insolubleprotein, [such as alpha protein or soya protein] between about [80] 80and 95 parts of Water, between about 5 and [60] 60 parts of a liquidhydrocarbon, and

sufficient dissolved water soluble alkali to dissolve said protein. [andbetween 10 and 90 parts of a gum pigment mixture, where the mixture ismade up of] The suspension contains between about 5 and 75 parts ofpaper pigment. between about 5 and 75 parts of dissolved water solublegum, and between about and 95 parts of water. The water soluble gum,which I prefer to use is animal glue, and I prefer to use soya proteinas the alkali soluble, water insoluble protein, however, I find thatcasein can also be used to good advantage. The liquid hydrocarbon [whichis used, and] which I prefer to use is diesel oil, although kerosene orhigher boiling liquid hydrocarbon materials can be used in practising myinvention.

I make my emulsions in the conventional manner, as taught, for example,by Kress et al. My suspensions may be prepared by first dissolving thewater soluble gum in water and then adding thereto a previously preparedaqueous dispersion of the pigment. It will be appreciated that thepigment can first be added to the water and then the gum added, or thepigment and gum can be added together. I like to use heat to promote gumdissolution and internzixing of pigment with gum. Optionally, inpreparing paper compositions of the invention, a gum can be dissolved inthe water phase of the emulsion before or after mixing the suspensionwith the emulsion. The emulsion can be admixed with the suspension byany conventional means. While the respective compositions of theemulsion and of the suspension can vary widely, I maintain the watersoluble gum to alkali soluble, water insoluble protein ratio withinfixed ranges in my emulsion-suspension coating compositions (seestatement below concerning weight ratio of gum to protein). The productemulsion-suspension is generally used rather quickly followingpreparation, and I have observed no particular stability or storageproblems.

As indicated, the compositions of this invention can be coated uponpaper using conventional paper coating equipment.

The following examples will serve to illustrate preferred embodiments ofmy invention and the methods followed in the practice thereof.

Those skilled in the art will appreciate that many variations andmodifications are possible within the teachings of the specificationwithout departing from the spirit and scope of this invention.

Example I.A paper coating composition was made up by dissolving 20pounds of alpha protein in ammonial solution. The water content of thesolution was adjusted so that the solids therein amount to 20% of thesolution. This solution is then allowed to cool to room temperature.Twenty pounds of the solution is then weighed out of the mass and twelvepounds of glue, animal glue, is added and the mixture is stirred untilthe glue is dissolved. To this mixture 10 pounds of diesel oil is added,and the mixture is agitated by a high speed mixer to form an oilin-wateremulsion. In a separate container, 8 pounds of predispersed clay, 8pounds of potato dextrin, 16 pounds of water are mixed together withagitation [and heat] and are heated to thoroughly intermix the potatodcxtrin with the pigment (i.e., the clay) to form a suspension and todissolve (i.e., gelatinize) the potato dextrin. The mass is then allowedto cool to room temperature. The mixture of potato dextrin, clay andwater are then added to the protein, glue and oil emulsion, while themass is being agitated by a high-speed mixer, such as a Lightning mixer.After the addition, the mass is cooled, and it is then ready to apply topaper with standard coating equipment. The resulting emulsion-suspensionis applied to a precoated base stock with a #20 Myer rod and the paperis dried. The coated paper product has good opacity, brightness, inkreceptivity, and gloss.

Example II.About 200 pounds of casein protein was weighed into about 900pounds of water. To enhance the [swelling] dissolution of protein,approximately 7 pounds of borax and about 20 pounds of 26 B6. NH OH wasadded. During the addition the entire mass was being agitated by threehigh-speed mixers, and the mass was heated to F. The agitation continuedfor about 45 minutes with the heat turned off, and the temperature roseto F. and then proceeded to cool to 98 F. The resulting mixture containsthe alkali soluble, water insoluble protein dissolved in alkalineaqueous solution. This mixture was added slowly to 500 pounds ofpetroleum hydrocarbon (diesel oil) with a flash point of 162 F. The masswas agitated during this addition and an oil-in-water emulsion wasproduced.

Simultaneously, a second mixture consisting of a water solution of gumand pigment particles suspended therein and comprising 700 pounds ofwater, 100 pounds of calcium carbonate, 100 pounds of talc, 100 poundsof titanium dioxide and 200 pounds of predispersed clay andapproximately 900 pounds of animal glue was prepared by mixing thesematerials together in the water and applyplying a suflicient heat todissolve the animal glue and promote intermixing of the pigment with theglue. The

mixture of gum and pigment is heated in the temperature range indicatedwith simultaneous agitation of the mixture to promote dispersion of thepigment particles until the glue is dissolved. This second mixture wasthen added to the protein, oil, and Water mixture and the mixing wascontinued until a creamy, smooth, uniform pigmented emulsion resulted.The resulting emulsion-suspension was applied to a precoated base stockwith a #20 Myer rod, and the paper was dried. The resulting product hadgood opacity, brightness, and ink-receptivity, and a gloss favorablycomparable with cast coatings.

Any of a wide range of hydrocarbons, including the petroleum distillatesmay be used for the purpose of my invention. I prefer to use thepetroleum distillates which are colorless hydrocarbons and have flashpoints between about 100 F. and 250 F. Of course, petroleum distillatesor other hydrocarbons having higher or lower flash points can be used.Although a colorless hydrocarbon is preferred, I find that hydrocarbonshaving small amounts of color can also be used, providing the color isnot so intense as to effect the brightness of the coated paper.

The pigments which are used should be selected from materials havingaverage particle sizes not greater than about 100 microns (in any onedimension) since materials having larger particle sizes are difiicult tocoat smoothly on the surface of paper. [Paper pigments, such as calciumcarbonate, chalk, or talc can be used alone or in combination with eachother. Another suitable pigment is walnut flour] The order of adding thepigment to the emulsion is critical. [It must be added with the watersoluble gum (Le. the animal glue) as the mass is being agitated, so thatthe protein will precipitate on and adhere to the surface of thepigment] The paper pigment must first be suspended in an aqueoussolution of a water soluble gum before being mixed with the hydrocarbonliquitl-in-water emulsion containing dissolved alkali soluble, waterinsoluble protein. I like to mix the emulsion with the suspension, orvice versa, while vigorously agitating the resulting mixture to promotecomplex mixing.

Certain emulsifying agents such as ammonium [oliate] oleate or the likemay be used to advantage in preparing the emulsions in accordance withmy procedure. [However, these materials are not essential, and apartfrom facilitating the emulsification of oil and water, they do notenhance the compositions made in accordance with my invention] Boraxand/or sodium hydroxide, or other alkali materials may be added tosolubilize the protein where water insoluble proteins are used, andthese alkali materials provide sufficient surface activity between theoil and water to aid emulsification of the ingredients.

The ratio of water soluble gums to protein can be varied from to 150%,depending upon the results [required] desired. Similarly, in preferredformulations, [The] the amount of water soluble gum in relation to theamount of pigment must be at least of gum to pigment. [Other gums, suchas methyl cellulose, polyvinyl alcohol and the like can be used, andother protein material besides casein and soya flour can be used] Thephysical and chemical nature of this composition is not clearlyunderstood. It is believed that the oilprotein-water mixture results inthe formation of small, individual particles of spongy protein, whichreadily accept ink. The addition of [glue] water dissolved gum to thepigment causes the pores of the pigment to be closed, thereby allowingthe spongy protein to coat the surface of the pigment, resulting in acoating which is essentially this spongy protein material, which givesthe brightness, opacity, and other desired properties, including gloss,and printability. It has been found that the coating has the ability toreadily accept ink and also has good varnish hold out, yielding anexcellent high-gloss print and reducing the amount of ink required forcomplete coverage.

It will be appreciated that in using a composition of the invention forcoating a paper, one first coats the paper with one of my compositionsand then dries same. The so-eoated sheet bears a thin layer of acoherent mixture of water soluble gum, allrali soluble, water insolubleprotein, and paper pigment, said coherent mixture being characterized byhaving a weight ratio of said gum to said protein of from about 10% to150% and by having a weight ratio of gum to pigment of at least about20%.

Having thus described my invention, I claim:

[1. A paper coating composition which consists essentially of asuspension of a paper pigment and finely subdivided particles of proteinin a liquid hydrocarbon-water emulsion, said protein and pigment forminga co-precipitate on the breaking of the emulsion with the particles ofprotein adhering to the pigment, said suspension consisting essentiallyof a dispersion of from 5 to 20 parts of an alkali soluble waterinsoluble protein selected from the group consisting of alpha protein,soya protein and casein and mixtures and equivalents thereof, between 80and 95 parts of Water, between 5 and 60 parts of a liquid hydrocarbonhaving a flash point between 100 F. and 250 F. and between 10 and 95parts of a gum pigment mixture where said gum pigment mixture is made upof between 5 and parts of a paper pigment, between 5 and 75 parts of asoluble gum selected from the group consisting of animal glue, methylcellulose and polyvinyl alcohol and mixtures and equivalents thereof andbetween 40 and 95 parts of water.]

[2. A pigmented paper coating composition comprising a co-precipitate ofpigment and protein from a suspension which is made up essentially bypreparing a first mixture of an alkali soluble protein selected from thegroup consisting of alpha protein, soya protein and casein and mixturesand equivalents thereof, a liquid petroleum hydrocarbon having a flashpoint between 100 F. and 250 F. and water in the ratio of. 5 to 20 partsof alkali soluble protein, between 5 and 60 parts of liquid hydrocarbon,and between and parts of water, preparing a second mixture of paperpigment, water soluble gum selected from the group consisting of animalglue, methyl cel lulose and polyvinyl alcohol and mixtures andequivalents thereof and water in the ratio of 5 and 75 parts of pigment,5 and 75 parts of gum, and 40 to 95 parts of water, adding the secondmixture to the first and agitating the mass to form an emulsionsuspension from which the coprecipitate is yielded when the emulsion isbroken] [3. The product of claim 1 in which the pigment has a particlesize of less than microns] [4. The product of claim 2 in which thepigment has a particle size of less than 100 microns] [5. A process of.manufacturing a coating composition for paper which comprises forming afirst mixture by adding 5 to 20 parts of an alkali soluble proteinselected from the group consisting of alpha protein, soya protein andcasein to between 80 and 95 parts of water, adjusting the pH of themixture to above 7, agitating the mixture while adding between 5 and 60parts of a liquid hydrocarbon having a flash point of between 100 F. and250 F. to form an emulsion, forming a second mixture by adding 5 to 75parts of a water soluble gum selected from the group consisting ofanimal glue, methyl cellulose and polyvinyl alcohol to between 40 and 95parts of water and adding 5 to 75 parts of a paper pigment and addingthe second mixture to the first mixture to form a pigmented emulsion] 6.In a process for making a paper coating composition, the steps of:

(a) dissolving between about 5 and 20 parts by weight of soya protein inbetween about 80 and 95 parts by weight of water containing suflicientdissolved alkali to solubilize said protein, thereby to form a firstsolution,

(b) emulsifying in said first solution between about and 60 parts byweight of liquid hydrocarbon having a flash point between about 100 and250 F., to form an emulsion,

(c) dissolving between about 5 and 75 parts by weight of animal glue inbetween about 40 and 95 parts by weight of water to form a secondsolution,

((1') dispersing in said second solution between about 5 and 75 parts byweight of coating clay to form a suspension, and

(e) mixing together said emulsion and said suspen sion to form ahomogeneous mixture.

7. In a process for making a paper coating composition, the steps of:

(a) dissolving between about 5 and parts by weight of casein in betweenabout 80 and 95 parts by weight of water containing dissolved thereinsufficient alkali to dissolve said casein and thereby form a firstsolution,

(b) emulsifying in said first solution between about 5 and 60 parts byweight of liquid hydrocarbon having a flash point between 100 and 250F.,

(c) dissolving between about 5 and 75 parts by weight of animal glue inbetween about 40 and 95 parts by weight of water to form a secondsolution,

(d) dispersing in said second solution between about 5 and 75 parts byweight of paper pigment, and

(e) mixing together said emulsion and said suspension to form ahomogeneous mixture.

8. In a process for making a paper coating composition, the steps of:

(a) dissolving between about 5 and 20 parts by weight of alkali-soluble,water-insoluble protein selected from the group consisting of alphaprotein, soya protein, and casein, in between about 80 and 95 parts byweight of water containing dissolved therein sufficient alkali todissolve said protein and thereby form a first solution,

(b) emulsifying in said first solution between about 5 and 60 parts byweight of liquid hydrocarbon,

(c) dissolving between about 5 and 75 parts by weight of water-solublegum selected from the group consisting of animal glue, vegetable glue,methyl cellulose, and polyvinyl alcohol, in between about 50 and 95parts by weight of water to form a second solution,

(d) dispersing in said second solution between about 5 and 75 parts byweight of paper pigment, and (e) mixing together said emulsion and saidsuspension to form a homogeneous mixture.

9. A paper coating composition produced by mixing an emulsion with asuspension, said emulsion consisting essentially of:

(a) between 80 and 95 parts by weight of water,

(b) between 5 and 20 parts by weight of dissolved alkali-soluble,water-insoluble protein selected front the group consisting of alphaprotein, soya protein, and casein, and

(c) between 5 and 60 parts by weight of liquid hydrocarbon, said liquidhydrocarbon being dispersed throughout said water; and

said suspension consisting essentially of:

(d) between 40 and 95 parts by weight of water,

(e) between 5 and 75 parts by weight of dispersed paper pigmentthroughout said water in the form of finely divided particles, and

(1) between 5 and parts by weight of a watersoluble gum selected fromthe group consisting of animal glue, vegetable glue, methyl cellulose,and polyvinyl alcohol, so that the amount of gum in relation to theamount of pigment is at least 20% of gum to pigment;

the amounts of the suspension and of the emulsion being such that theratio of gum to protein is between 10% and 150%.

[0. A paper coating composition in accordance with claim 9 wherein thepigment is composed of particles having average sizes of less than 100microns.

1]. A paper coating composition in accordance with claim 9 wherein saidprotein is soya protein.

12. A paper coating composition in accordance with claim 9 wherein saidprotein is casein.

13. A paper coating composition in accordance with claim 9 wherein saidprotein is alpha protein.

14. A paper coating composition in accordance with claim 9 wherein saidprotein is soya protein and said paper pigment is clay.

15. A paper coating composition in accordance with claim 9 wherein saidwater-soluble gum is animal glue.

16. A paper coating composition produced by mixing an emulsion with asuspension, said emulsion consisting essentially of:

(a) between and parts by weight of water,

(b) between 5 and 20 parts by weight of dissolved soya protein, and

(c) between 5 and ()0 parts by weight of liquid hydrocarbon having aflash point between and 250 F., said liquid hydrocarbon being dispersedthroughout said water; and

said suspension consisting essentially of:

(d) between 40 and 95 parts by weight of water,

(e) between 5 and 75 parts by weight of dispersed coating claythroughout said water in the form of finely divided particles, and

(f) between 5 and 75 parts by weight of dissolved animal glue so thatthe amount of glue in relation to the amount of clay is at least 20% ofglue to clay, and

the amounts of the suspension and of the emulsion being such that theratio of glue to protein is between 10% and 17. A paper coated on atleast one surface with the composition of claim 9.

References Cited by the Examiner The following references, cited by theExaminer, are of record in the patented file of this patent or theoriginal patent.

UNITED STATES PATENTS 175,683 4/76 Fetzer 106129 1,816,978 8/31 Knight106135 2,059,465 11/36 Kress cl :1]. l()6134 2,185,859 1/40 Massey106139 2,245,499 6/41 Rcichel ct a], 106128 2,537,055 1/51 Huon et al.106135 2,933,406 4/60 Salzbcrg 106125 2,995,414 8/61 Paul 1()61393,108,009 10/63 Clancy et al. 106-135 ALEXANDER H. BRODMERKEL, PrhnaryExaminer.

MORRIS LIEBMAN, Examiner.

